import java.util.HashSet;
import java.util.Iterator;
import java.util.Random;
public class TestHashSet {
public static void main(String[] args) {
Random r = new Random();
HashSet hs1 = new HashSet();
for(int i=0; i<3000; i++){
hs1.add(r.nextInt(10));
}
Iterator it1 = hs1.iterator();
while(it1.hasNext()){
System.out.print(it1.next()+" ");
}
}
}
//由于 HashSet 不能重复，所以只有10个数在里面，按哈希排序
2 4 9 8 6 1 3 7 5 0
/*
* 测试TreeSet 的比较器，
* 在有自己的比较器的情况下，如何实现Comparable接口
*/
import java.util.*;
class Teacher{
int id;
String name;
int age;
public Teacher() {}
public Teacher(int id, String name, int age) {
this.id = id;
this.name = name;
this.age = age;
}
public int getId() { return id; }
public void setId(int id) {this.id = id; }
public String getName() { return name;}
public void setName(String name) { this.name = name;}
public int getAge() {return age;}
public void setAge(int age) {this.age = age;}
public int TeacherComparator(Object o){
Teacher t1 = (Teacher) o;
if(t1.getId() > id){return 1;}
else if (t1.getId() < id){return -1;}
return 0;
}
}
class TreeSet{
}
class Test {
public static void main(String[] args) {
String s1 = new String("aaa");
String s2 = new String("bbb");
String s3 = new String("aaa");
System.out.println(s1==s3);
System.out.println(s1.equals(s3));
HashSet hs = new HashSet();
hs.add(s1);
hs.add(s2);
hs.add(s3);
Iterator it = hs.iterator();
while(it.hasNext()){
System.out.println(it.next());
System.out.printf("%x\n",s1.hashCode());
System.out.printf("%x\n",s2.hashCode());
System.out.printf("%x\n",s3.hashCode());
}
}
1. 在Map中，以name作Key，以Student类 作Velue，写一个HashMap
import java.util.*;
class Student{
int id;
String name;
int age;
public Student() {}
public Student( int id, String name, int age) {
this.id = id;
this.name = name;
this.age = age;
}
public int getId() {return id;}
public void setId(int id) {this.id = id;}
public String getName() {return name;}
public void setName(String name) {this.name = name;}
public int getAge() {return age;}
public void setAge(int age) {this.age = age;}
}
class TestHashMap{
public static void main(String[] args) {
HashMap hm = new HashMap();
Student s1 = new Student(1,"jacky",19);
hm.put("jacky",s1);
hm.put("tom",new Student(2,"tom",21));
hm.put("kitty",new Student(3,"kitty",17));
Iterator it = hm.keySet().iterator();
while(it.hasNext()){
Object key = it.next();
Student value = (Student) hm.get(key);
System.out.println(key+":id="+value.id+",age="+value.age);
}
System.out.println("=============================");
//比较 KeySet() 和 entrySet() 两种迭代方式
for(Iterator i1 = hm.entrySet().iterator(); i1.hasNext(); )
{ Map.Entry me = (Map.Entry) i1.next();
Student s = (Student) me.getValue();
System.out.println(me.getKey()+": id="+s.id+" age="+s.age);
}
}
}
day13 homework
1.
/**********************************************************************************
自己写一个栈: ( 先进后出 )
建议底层用LinkedList实现
参照 java.util.Stack
方法: boolean empty() 测试堆栈是否为空。
E peek() 查看栈顶对象而不移除它。
E pop() 移除栈顶对象并作为此函数的值返回该对象。
E push(E item) 把项压入栈顶。
int search(Object o) 返回对象在栈中的位置，以 1 为基数。
***************************************************************************************/
//不能用继承，因为它破坏封装。只需调用即可
import java.util.LinkedList;
class MyStack
private LinkedList
public boolean empty() {return list.isEmpty()